My eldest daughter (22) is truly a lovely lass. She is good-natured and would do anything to help anyone. She's the apple of my eye. She also has high functioning autism and I'm wary of people taking advantage of her.
A couple of weeks ago, she ended her 4 year relationship with her boyfriend. He couldn't have asked for a more loyal and understanding girlfriend, but he took her for granted and was borderline abusive towards her. I was glad when it ended because there were many red flags. I always kept the communication open around this when they were together. I am proud of her for being strong enough to end it and she hasn't looked back 
She also has a male ex work colleague friend, who helped her to see that her boyfriend's behaviour was unacceptable. They seem to have built a nice, purely platonic friendship and my daughter is happy to have him in her life. Her ex boyfriend wouldn't have 'allowed' them to be friends if still on the scene.
This man quit his job at my daughter's work and is living in a hostel. She has helped him out this week by baking him a cake for his birthday and giving him a heater (one that we no longer needed at home) when the heating at the hostel broke down. To be fair, the friendship does seem to be two-sided as he treated her to dinner through the week.
The curfew for the hostel is 11pm, and this man would like to go clubbing with friends tonight. The friends can't meet up until later, and it wouldn't give him long until he needs to return to the hostel. Without asking me, my daughter told him he could stay at our place tonight.
Not thinking this would be a problem for me, she then decided to run it by me! I have said no. I also have two teenage daughters to consider, and we haven't met this man. My eldest has flounced off, unhappy with my decision.
AIBU? Her friend is by all accounts a lovely person, but I am worried that my daughter is casting herself in the role of rescuer once again ... something that she did with her ex.
I've gently broached this with her, and have explained that dire straits would perhaps be a different matter, but the man's social life is for HIM to navigate.
She says that I should trust her judgement on this, and that I'd be different with a female friend. I openly admitted that this was exactly right 
I'm struggling a bit as she and I never usually fall out. But I think I'm doing the right thing. Aren't I?